Hologram and holgraphic viewing device incorporating it

ABSTRACT

The invention relates to a hologram that enables two or more different images to be simultaneously reconstructed even in a state where the hologram is fixed in terms of relative position with respect to an eye, and a holographic viewing device that incorporates it. The hologram  14  is fabricated by applying Fourier transform to a plurality of input image to obtain a plurality of corresponding Fourier transform images  13 - 1, 13 - 2  and arraying the Fourier transform images  13 - 1, 13 - 2  on the same plane according to a given two-dimensional array principle into a computer-generated hologram. When a plurality of point light sources  23   1  to  23   9  located behind the hologram  14  are viewed through the hologram  14 , a plurality of images are simultaneously and parallel reconstructed ( 28 ) in correspondence to the array positions of the plurality of Fourier transform images.

BACKGROUND OF THE INVENTION

The present invention relates generally to a hologram and a holographicviewing device incorporating it, and more particularly to a holographicviewing device with a built-in computer-generated hologram set up in theform of a transmission type Fourier transform hologram.

Patent Publication 1 comes up with holographic eyeglasses constructed asshown in the perspective view of FIG. 16( a). More specifically, twotransmission type holograms 2 and 3 are fitted in a binocular frameworkof an eyeglass frame 1. As a scene containing light sources 4, 5, 6 and7, each of small area, as shown in FIG. 16( b), is viewed with theeyeglasses using the transmission type holograms 2 and 3, for instance,it looks as shown in FIG. 16( c). In other words, it looks as if thesmall-area light sources 4, 5, 6 and 7 in the actual scene of FIG. 16(b) were replaced with pre-selected words “NOEL” 8, 9, and 11,respectively. For the transmission holograms 2 and 3 having suchfeatures, Fourier transform (Fraunhofer) holograms having the aforesaidwords “NOEL” are used in the form of computer-generated holograms.

A little more explanation is given of the transmission holograms 2 and3. Suppose now that transmission type hologram 21 stands for thetransmission type holograms 2 and 3, and a (small-area) point lightsource 23 is located behind the transmission type hologram 21, as shownin FIG. 14( a). Then, as the point light source 23 is viewed with an eye22 through the transmission type hologram 21, one image is reconstructedcorresponding to the point light source 23 behind that transmission typehologram 21. FIG. 14( b) is a plan view of a unit hologram 24 that formsa part of the transmission type hologram 21. As shown, nine elementholograms 24 ₁, each comprising a transmission type Fourier transformhologram, are lined up parallel with one another into the unit hologram24, and the transmission type hologram 21 is assembled by arranging amultiplicity of such unit holograms 24 in rows and columns. FIG. 14( c)is illustrative of one exemplary reconstructed image 25 reconstructedupon viewing the point light source 23 through the transmission typehologram 21, which corresponds to the word “NOEL” in FIG. 16( b). Inthis case, the image has a crescent form.

As many images as the point light sources are reconstructed through thetransmission hologram 21 comprising such unit holograms 24 as shown inFIG. 14( b) (=FIG. 15( b)). As nine point light sources 23 ₁ to 23 ₉located behind the transmission hologram 21 are viewed through thetransmission hologram 21 as shown typically in FIG. 15( a), it allows animage with nine identical (crescent) images lined up in rows and columnsto be reconstructed and seen.

On the other hand, Patent Publication 3 proposes that a plurality ofunit holograms 24 for reconstructing mutually different images areparallel arranged into a transmission type hologram, and the position ofan eye with respect to that transmission type hologram is so varied thata single image differing depending on the light sources behind thattransmission type hologram is reconstructed.

-   Patent Publication 1-   U.S. Pat. No. 5,546,198-   Patent Publication 2-   JP(A)2004-126535-   Patent Publication 3-   JP(A)10-282870

However, such transmission type holograms as briefed above are shy ofvariations and interest, because, as long as the relative position withrespect to the eye is fixed, as many single identical images as pointlight sources are only reconstructed.

SUMMARY OF THE INVENTION

In view of such problems with the prior art, the primary object of thisinvention is to provide a hologram that enables two or more varyingimages to be simultaneously reconstructed even in a state where it isfixed in terms of relative position with respect to an eye, and aholographic viewing device that incorporates it.

According to one aspect of the invention, the aforesaid object isaccomplished by the provision of a hologram, characterized by beingfabricated by applying Fourier transform to a plurality of input imageto obtain a plurality of corresponding Fourier transform images andarraying said Fourier transform images on the same plane according to agiven two-dimensional array principle into a computer-generatedhologram, and in that when a plurality of point light sources locatedbehind said hologram are viewed through said hologram, a plurality ofimages are simultaneously and parallel reconstructed in correspondenceto the array positions of said plurality of Fourier transform images.

In one preferable embodiment of the invention, said hologram could be ofeither the phase type (Patent Publication 2) or the amplitude type(Patent Publication 3).

In this embodiment, it is desired that said plurality of Fouriertransform images be closely arrayed in a region of given shape on thebasis of the two-dimensional array principle.

In another preferable embodiment of the invention, said Fouriertransform image corresponding to each input image is arrayed alone orparallel in two or more into a unit hologram corresponding to each inputimage, and unit holograms corresponding to a plurality of input imagesare arrayed on the same plane on the basis of a given two-dimensionalarray principle into a computer-generated hologram.

In yet another preferable embodiment of the invention, it is desiredthat said plurality of unit holograms be configured into any shapehaving a maximum diameter of 4 mm to 2 L·tan 10° inclusive provided thatL is the distance from a viewer's eye to the hologram.

The invention also encompasses a holographic viewing device in which acomputer-generated hologram set up as a transmission type Fouriertransform hologram is fitted in a frame, wherein said computer-generatedhologram is any one of the aforesaid holograms.

According to the invention, it is possible to provide a hologram thatenables a plurality of images to be simultaneously and parallelreconstructed even in a state where it is fixed in terms of a relativeposition with respect to an eye, and a holographic viewing device thatincorporates it.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises the features of construction,combinations of elements, and arrangement of parts which will beexemplified in the construction hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a flowchart of one hologram fabrication process accordingto the invention, and FIG. 1( b) is illustrative in schematic of thatflowchart.

FIGS. 2( a)-(c) is illustrative of how to reconstruct images with thehologram fabricated according to FIG. 1.

FIG. 3 is illustrative of the positions of point light sources at whicheach image reconstructed from the hologram can be seen and a region inwhich each reconstructed image can be seen.

FIG. 4 is illustrative of the one-dimensional direction region of ahologram entering the angle of view of an eye when the hologram—locatedspaced away from the eye by a given distance—is viewed as shown in FIG.3.

FIG. 5 is illustrative of the maximum diameter of a hologram in a casewhere the hologram is positioned by fingers in front of the eye.

FIG. 6 is illustrative of a distance from an eye to a window glass andthe maximum diameter of unit holograms in a typical case where ahologram is applied to the window glass.

FIG. 7 is illustrative of one example of the array of unit hologrampatterns, which enables two reconstructed images to be seen at the sametime.

FIG. 8 is illustrative of another example of the array of unit hologrampatterns, which enables two reconstructed images to be seen at the sametime.

FIGS. 9( a)-(b) is illustrative of yet another example of the array ofunit hologram patterns, which enables two reconstructed images to beseen at the same time.

FIGS. 10( a)-(b) is illustrative of a further example of the array ofunit hologram patterns, which enables two reconstructed images to beseen at the same time.

FIGS. 11( a)-(b) is illustrative of a further example of the array ofunit hologram patterns, which enables two reconstructed images to beseen at the same time.

FIG. 12 is illustrative of one example of the array of unit hologrampatterns, which enables three reconstructed images to be seen at thesame time.

FIG. 13 is illustrative of exemplary unit holograms of various shapesand sizes usable herein.

FIGS. 14( a)-(c) is illustrative of how one image is reconstructed perlight source in the prior art.

FIGS. 15( a)-(c) is illustrative of how as many images as a plurality oflight sources are reconstructed in the prior art.

FIGS. 16( a)-(c) is illustrative of prior art holographic eyeglasses andhow they work.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1( a) is a flowchart illustrative of one hologram fabricationprocess according to the invention, and FIG. 1( b) is illustrative inschematic of that flowchart. First of all, a plurality of input images41 and 42 are fabricated on a computer (step 101). For instance, theinput image 41 has a crescent pattern a, and the input image 42 has astellar pattern b.

Then, on the computer, Fourier transform is applied to each input image41, 42 to fabricate a Fourier transform image 51, 52 (step 102). EachFourier transform image 51, 52 is binarized or multi-digitalized (step103). In FIG. 1( b), numeral reference 61 is a Fourier transform imagethat is multi-digitalized in correspondence to the input image 41 (adiffraction optical element; an element hologram), and 62 is a Fouriertransform image (a diffraction optical element; and element hologram)that is multi-digitalized in correspondence to the input image 42.

Then, the image to be reconstructed is simulated (step 104). For thissimulation, inverse Fourier transform is applied to themulti-digitalized Fourier transform images 61, 62 to obtain therespective Fourier transform images 71, 72, whereby whether or notappropriate processing has occurred at each step is checked out.

Then, each multi-digitalized Fourier transform image (element hologram)61, 62 is arrayed up to the desired range (step 105). For instance,binarized Fourier transform images 61, 62 are arrayed four per row andcolumn to obtain unit holograms 13-1(A) and 13-2(B).

Then, the unit holograms 13-1 and 13-2 are arrayed on the basis of thegiven two-dimensional array principle (step 106) to fabricate acomputer-generated hologram 14. In the computer-generated hologram 14,the unit holograms 13-1 and 13-2 are lined up in a checker flag pattern,as shown in FIG. 1( b). It is here noted that the two-dimensionallyarrayed unit holograms 13-1 and 13-2 are each in a rectangular form.

The thus arrayed computer-generated hologram 14 output is produced ontoa film by means of a laser scanner or the like (step 107).Alternatively, that computer-generated hologram 14 could be fabricatedby a multi-digitalization technique using a semiconductor fabricationprocess and etching as set forth in Patent Publication 2.

FIG. 2 is illustrative of how to reconstruct images using the thusobtained computer-generated hologram 14. In FIG. 2( a), referencenumeral 22 is the eye of a viewer, and 23 ₁ to 23 ₉ are nine point lightsources (of small area). As the hologram 14, behind which the nine pointlight sources 23 ₁ to 23 ₉ are located, is viewed with the viewer's eye22, it allows the viewer to see a reconstructed image 28 in which, astypically shown in FIG. 2( c), a center image a (of crescent pattern) issurrounded with images b (of stellar pattern), corresponding to unitholograms 13-1 and 13-2 (FIG. 2( b)) at positions where straight linesconnecting the center of the pupil of the eye 22 with the point lightsources cross the hologram 14.

FIG. 3 is illustrative of the position of the point light source whereeach reconstructed image can be seen from the thus obtained hologramwith the left eye or the right eye and a region where each reconstructedimage can be seen. In FIG. 3, reference 22 stands for the left eye orthe right eye; 23 ₄, 23 ₅ and 23 ₆ indicate the positions of the pointlight sources where each reconstructed image can be seen; 32 representsa region where the (crescent) reconstructed image a can be seen; and 33shows a region where the (stellar) image b can be seen. Thus, the viewercan see the (crescent) image a and (stellar) images b reconstructed atthe regions corresponding to the unit holograms 13-1 and 13-2 where thestraight lines connecting the center of the pupil of the viewer's eye 22with the point light sources 23 ₄, 23 ₅ and 23 ₆. It is here noted thatthe unit hologram 13-1 and the unit hologram 13-2 are each composed ofone or more element holograms 61 and 62 having a maximum diameter of 4mm to 2 L·tan 10° inclusive where L is the distance from the eye 22 tothe hologram 14.

The range of 4 mm to 2 L·tan 10° for the maximum diameter of the unitholograms 13-1 and 13-2 is empirically determined throughexperimentation. The lower limit to the maximum diameter of the unithologram 13-1, 13-2 is set at 4 mm for the reason that the human eye 22for use with that hologram 14 has a pupil diameter of about 4 mm. Inother words, unless the maximum diameter of the unit hologram 13-1, 13-2exceeds that pupil diameter of 4 mm, there is then a possibility thatthe adjacent two unit holograms 13-1 and 13-2 may enter the pupilsimultaneously, failing to see the images a and b due to the unitholograms 13-1 and 13-2 at the same time yet in a separate fashion. Theupper limit of 2 L·tan 10° to the maximum diameter of the unit hologram13-1, 13-2 could be determined as follows.

Simple experimentation shows that the angle of view, at which the humaneye 22 can see two mutually spaced objects at the same time with norelative movement, is about 20°. FIG. 4 is illustrative of theone-dimensional direction region of a hologram 14 entering that angle ofview when the hologram 14 spaced away from the eye 22 by a distance L isviewed as shown in FIG. 3, indicating that the one-dimensional directionregion is given by 2 L·tan 10°. FIG. 4 also indicates that to contain atleast two unit holograms 13-1 and 13-2 in this range, the upper limit totheir maximum diameter is 2 L·tan 10°.

FIG. 5 is illustrative of a distance L from an eye 22 to a hologram 14and the upper limit of 2 L·tan 10° to the maximum diameter of unitholograms 13-1 and 13-2 in a typical case where the hologram 14 ispositioned by fingers in front of the eye 22, indicating that thehologram 14 can be brought to a position about 12 mm before the eye 22;the maximum diameter of the unit holograms 13-1 and 13-2 is in the rangeof 4.0 to 4.2 mm.

FIG. 6 illustrative of a distance L from an eye 22 to a window glass(hologram 14) and the upper limit of 2 L·tan 10° to the maximum diameterof unit holograms 13-1 and 13-2 in a typical case where the hologram 14is applied to the window glass, indicating that the hologram 14 can beplaced at a position about 30 cm before the eye 22; the maximum diameterof the unit holograms 13-1 and 13-2 is in the range of 4.0 mm to 10 cm.

From the above considerations, it is found that when the hologram 14 ofthe invention is used in the form of eyeglasses, window glass or thelike while located in front of the eye 22, it is of importance to allowa plurality of unit holograms 13-1 and 13-2 provided in the hologram 14to be reflected in the retina of the eye 22 simultaneously in a separatefashion. From this, it is desired that one maximum diameter of the unitholograms 13-1 and 13-2 be in the range of 4 mm that is the pupildiameter of the human eye 22 up to the size that enters the angle ofview of 20° of the human eye 22, namely, 2 L·tan 10° (where L is thedistance from the eye 22 to the hologram 14). Otherwise, it will beimpossible to view the image a (crescent pattern) and the images b(stellar pattern) at the same time without movement of the eye.

The two-dimensional array principle for unit holograms A (13-1) and B(13-2) in the hologram 14 of the invention is now explained. FIG. 7 isillustrative of an example of the hologram 14 wherein unit hologram Apatterns and unit hologram B patterns are lined up in cells, each ofsquare shape, arrayed in a rectangular chessboard form, as in FIG. 2.

FIG. 8 is illustrative of a possible modification to the array of FIG.7, wherein every one row is displaced at a half pitch with respect torows just above and below it.

It is here noted that individual unit holograms could be each of notonly rectangular shape but also any desired shape such as triangular orhexagonal shape, some of which are described below.

FIG. 9( a) is illustrative of an example of the hologram 14, whereinunit hologram A patterns of erected regular triangle shape and unithologram B patterns of inverted regular triangle shape are alternatelyarrayed.

FIG. 9( b) is illustrative of a modification to FIG. 7, wherein unithologram A patterns are located in most of cells, each of square shape,arrayed in a square chessboard form, and unit hologram B patterns arelocated in cells that are found discretely and regularly in arow-and-column pattern.

FIG. 10( a) is illustrative of an example of the hologram 14, whereinten unit holograms A of regular pentagon shape are located in an annularform, and unit hologram B patterns are located in cells inside andoutside the annular form.

FIG. 10( b) is illustrative of an example of the hologram 14, whereinunit holograms A of regular hexagon shape are lined up in 0°, 60° and120° directions, and a unit hologram B pattern is located in a cell ofregular triangle shape between the unit holograms A of regular hexagonshape.

FIG. 11( a) is illustrative of an example of the hologram 14, whereincross-shaped unit holograms A are periodically located in such a way asto come in contact with each other in a row-and-column pattern, and aunit hologram B is located in an octagonal cell defined by fourcross-shaped unit holograms A.

FIG. 11( b) is illustrative of an example of the hologram 14, whereinannular unit holograms A are periodically located in such a way as tocome in contact with each other in a row-and-column pattern, and unitholograms B are located in each annular unit hologram A and a celldefined by four annular unit holograms A.

In the examples as mentioned above, two images a and b are used as theinput images. As shown in FIG. 12 as an example, however, a unithologram A pattern, a unit hologram B pattern and a unit hologram Cpattern for the reconstruction of three or more images a, b and c couldbe arrayed in cells, each of square shape, in a rectangular chessboardpattern according to any desired two-dimensional array principle.

It is understood that if two or more unit hologram patterns are arrayedat random rather than regularly, there can then be obtained a hologram14 capable of reconstructing a more attractive array of images.

In addition, the unit holograms A and B could be used in various shapesand sizes. FIG. 13 is illustrative of one exemplary hologram 14 to thisend. As shown, 8 unit holograms B are located around one square unithologram A of relatively large size, and they are comprised of fourrectangular ones and four L-shaped ones.

As described above, no particular limitation is imposed on the shape andtwo-dimensional array of unit holograms A, B, C, etc. for the hologram14 of the invention; unit holograms of various shapes could be arrayedaccording to any desired array method, and unit holograms for thereconstruction of the same image could be provided in combinations ofvarious shapes. However, the size of individual such unit hologramsshould preferably be such that, as described above, their maximumdiameter is in the range of 4 mm to 2 L·tan 10°.

The element hologram or holograms 61, 62 that form each unit hologram,too, could be arrayed alone or in any desired combination of a pluralityof shapes into unit holograms A, B, C and so on.

The hologram 14 as described above could be fitted in a binocularframework of an eyeglass frame 1 of FIG. 16( a) into a holographicviewing device or in another form of framework, for instance, a paperframe into a toy. Furthermore, the hologram 14 could be used whileapplied to a window glass.

While the hologram of the invention and the holographic viewing devicethat incorporates it have been explained with several embodiments, it isnoted that there could be various modifications to them. It is alsonoted that the hologram of the invention could be used with aholographic monocle.

1. A hologram, which is fabricated by applying Fourier transform to twoor more different input patterns to obtain a plurality of correspondingFourier transform images and arraying said Fourier transform images onthe same plane according to a given two-dimensional array principle intoa computer-generated hologram, wherein when a plurality of point lightsources located behind said hologram are viewed through said hologram,said two or more different patterns are simultaneously and parallelreconstructed in correspondence to array positions of said plurality ofFourier transform images, a first of said two or more different inputimages being reconstructed at a correspondence to a first of saidplurality of point light sources and a second of said two or moredifferent input images, different from said first of said two or moredifferent input images, being reconstructed at a correspondence to asecond of said plurality of point light sources, said first image notbeing reconstructed at the correspondence to said second of saidplurality of point light sources.
 2. The hologram according to claim 1,wherein said plurality of Fourier transform images are closely arrayedin a region of given shape on the basis of the two-dimensional arrayprinciple.
 3. A holographic viewing device in which a computer-generatedhologram set up as a transmission type Fourier transform hologram isfitted in a framework, wherein said computer-generated hologram is ahologram as recited in claim
 2. 4. A holographic viewing device in whicha computer-generated hologram set up as a transmission type Fouriertransform hologram is applied to a window glass, wherein saidcomputer-generated hologram is a hologram as recited in claim
 2. 5. Aholographic viewing device in which a computer-generated hologram set upas a transmission type Fourier transform hologram is fitted in aframework, wherein said computer-generated hologram is a hologram asrecited in claim
 1. 6. A holographic viewing device in which acomputer-generated hologram set up as a transmission type Fouriertransform hologram is applied to a window glass, wherein saidcomputer-generated hologram is a hologram as recited in claim
 1. 7. Thehologram according to claim 1, wherein said second image is not beingreconstructed at the correspondence to said first of said plurality ofpoint light sources.